A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a user drives a car equipped with a navigation function. Such a navigation system detects the position of the vehicle, and reads out map data pertaining to an area at the current vehicle position from a data storage medium, for example, a CD-ROM (compact disc read-only memory), a DVD (digital versatile disc), or a hard disc. Alternatively, such map data can be provided from a remote navigation server through a communication network such as radio transmission or Internet.
When a destination is set, the navigation system starts a route guidance function for setting a guided route from the start point to the destination. To determine the guided route to the destination, the navigation system calculates and determines an optimum route to the destination based on various parameters. For example, the guided route is determined based on the shortest way to reach the destination, the route preferring freeways to surface roads, the least expensive way to the destination, the route without using toll road, or the like.
During the route guidance, the navigation system reads the nodes data from the data storage medium such as DVD and successively stores the nodes data of road segments (expressed in longitude and latitude) constituting the guided route in a map memory. In the actual traveling, the node series stored in the map memory is searched for a portion of the guided route to be displayed in a map display area of the monitor screen, and the portion of the guided route is highlighted to be clearly distinguished from other routes.
When the vehicle is within a predetermined distance of an intersection it is approaching, an intersection guidance diagram (an enlarged or highlighted intersection diagram with an arrow indicating the direction in which the vehicle is to turn at the intersection) is displayed to inform a user of the desired one of roads or directions selectable at the intersection. Such route guidance by the navigation system is also given by voice instruction.
FIGS. 1A–1H show an example of overall procedure and screen display involved in the navigation system. FIG. 1A shows an example of locator map screen of the navigation system when the destination is not specified. Typically, the navigation system displays a street on which the vehicle (current vehicle position VP) is running on a map image and a name of the street. Other information such as a north pointer NP, a map scale and a current time may also be illustrated on the screen.
An example of process for specifying a destination in the navigation system through a point of interest (POI) search method is shown in FIG. 1B–1F. A main menu screen such as shown in FIG. 1B displays menu items including a “Destination” menu for entering the destination. When selecting “Destination”, the navigation system displays a “Find Destination by” screen as shown in FIG. 1C for specifying an input method for selecting the destination.
The “Find Destination By” screen lists various methods for selecting the destination including “Address” for specifying the city and address of the destination, “Intersection” for specifying the names of two streets which intersect with one another, and “Point of Interest (POI)” for selecting the programmed destination based on the name, category or telephone number. Other methods in the “Find Destination by” screen include “Recent Route” for specifying the destination based on the recent history of destinations saved in the navigation system, and “Address Book” for selecting the address of the destination out of the prescribed address list stored in the system.
When selecting, the “Point of Interest” method in FIG. 1C, the navigation system displays selection methods of point of interest (POI) either by “Place Name” or “Place Type” in FIG. 1D. The “Place Name” is to specify a name of POI, and the “Place Type” is to specify a category of POI. If the “Place Type” is selected in FIG. 1D, the navigation system lists categories of POIs as shown in FIG. 1E. The order of listing the categories may be arranged in, for example, an alphabetical order or an order of distance from the current position.
FIG. 1F shows a screen when the user has selected a “Fast Foods” category in the example of FIG. 1E. In this example, the screen includes a list of names of the fast food restaurants typically sorted by distance from the current destination. In this example, the user selects “Pizza Hut” as his destination. In FIG. 1G, the navigation system calculates and determines a guided route to the destination. After determining the guided route, the navigation system starts the route guidance as shown in FIG. 1H. Typically, the navigation system shows the intersection that is highlighted to show the next turn and a direction of the turn.
Suppose the navigation system is in the route guidance mode as shown in FIG. 2A to guide the user to the selected destination. During such a trip, the user may want to use the navigation system to other purposes, such as to search for a gas station or a restaurant on the way to the destination. For example, if the user wants to find a Japanese restaurant on the way to the destination, he has to change the screen of the navigation system to the POI search screen as shown in FIG. 2B. During such a search mode, the route guidance information such as FIG. 2A is unavailable and the user may not be able to turn at the appropriate intersection.
Similarly, as shown in FIGS. 3A and 3B, when the user changes the screen after the route guidance screen, the guidance information is not provided to the user. For example, when the user maneuvers the navigation system to view a menu screen (FIG. 3A) with menu bars 9 or a map image of a remote area (FIG. 3B), the user cannot see the route guidance information. Because the navigation system in the conventional technology cannot provide the route guidance information on the display in such a case, it has a disadvantage in that the user is confused in following the direction to reach the destination.